In recent years, with popularization of the Internet, a service that handles a content including large-capacity data such as a voice and a video is expanding, and therewith, a communication amount is rapidly increasing. In a communication line (hereinafter, abbreviated as a “line”) facility which provides an Internet service that handles the large capacity content, an optical communication technique capable of performing, for example, broadband and long-distance communication is used.
In the line facility, electrical signals from various types of information processing devices such as servers that provide an Internet service are multiplexed by a terminal device and thereafter is subjected to electrical-optical conversion. An optically converted signal light is transmitted to an opposite terminal device, for example, via an optical fiber constituting a transmission path.
The opposite terminal device causes the transmitted signal light to be subjected to optical-electrical conversion and thereby acquires a multiplexed electrical signal. The multiplexed electric signal is demultiplexed into individual electrical signals, and the demultiplexed electrical signals are received by various types of information processing devices.
In the terminal device and transmission path, depending on a demand for a line, a new facility may be added to an existing facility by using, for example, an optical wavelength division multiplexing technique and the like. In this case, a change of transmission quality as described below may occur.
When, for example, a line facility is added, in a transmission path configuring the line facility, light of a wavelength used for an intended communication is affected by light of an adjacent wavelength. Thereby, transmission quality in the transmission path may degrade. In a transmission path configuring a line facility, by using a chance in which a line facility has been added, an adverse influence such as interference is not produced on light of a wavelength used for an intended communication, for example, by transfer of light of an adjacent wavelength to another wavelength, and thereby transmission quality in the transmission path may be improved. An element or the like that transmits light used between terminal devices deteriorates over time, and thereby transmission quality in the transmission path may decrease.
It is necessary for a line facility that provides an Internet service to maintain predetermined quality over a long term and continuously provide the Internet, even when a line situation as described above changes. Therefore, a terminal device using the optical communication technique needs to be designed in such a way as to be able to maintain predetermined transmission quality by expecting in advance, from a stage of introducing the terminal device, addition to a facility in the future and a change of a line situation due to aging of the facility. In the terminal device using the optical communication technique, in order to maintain transmission quality, generally, a forward error correction (hereinafter, abbreviated as an “FEC method”) is used. The FEC method is one type of an error control method in data transmission and is a coding method in which, when coding data, a data transmitting side provides redundancy for the data, and thereby, without a request to the transmitting side for additional information, a receiving side detects and corrects an error of the data when decoding the data.
The above-described terminal device employs an FEC method (hereinafter, referred to also as a “coding method”) having an ability (error correction ability) of correcting a detected error of data in order to ensure predetermined transmission quality. However, in the FEC method, when a modification of the above-described line facility and a change of a line situation due to an aging change are considered in advance and an FEC method having a high error correction ability is fixedly used, by contrast, transmission efficiency may decrease and a processing delay and power consumption in a terminal device may increase.
As one example of such a technique, PTL 1 discloses a technique in which a receiving side of a digital transmission system monitors quality of a reception signal and selects an FEC method depending on the quality of the monitored reception signal, and thereby an error correction method of the receiving side and a transmitting side is switched on the basis of the selected FEC method. The digital transmission system in PTL 1 notifies a transmitting side of a change of transmission quality on a receiving side in order to switch an error correction method, notifies the receiving side of a switching timing of an error correction method from the transmitting side, transmits an acknowledge (ACK) signal from the receiving side to the transmitting side, and switches the error correction method. The digital transmission system in PTL 1 previously supplies a power source and a clock also to an error correction circuit of a switching destination in such a way that data to be transmitted/received are not missing.
As a related technique, PTL 2 discloses a technique for suppressing a variation of an error correction ability for each optical reception device due to an individual difference in production and aging deterioration of an identifier for identifying an electrical signal obtained by converting a received optical signal, by an optical reception device.
PTL 3 discloses a technique for suppressing, when an optical transmission device is added with an optical transmission device having a high error correction ability, an optical power of an output signal of the added optical transmission device to a level lower than an optical power of an output signal of the existing optical transmission device and thereby expanding a transmission capacity at a low cost.
PTL 4 discloses a technique in which an occurrence situation analysis unit that analyzes a data error in a digital signal processing device determines a future error occurrence frequency on the basis of information about a current error occurrence situation and peripheral information acquired from an error correction processing unit and a peripheral information analysis unit.